The rapid diffusion of Wireless Local Area Network (WLAN) access and the increasing demand for WLAN coverage is driving the installation of a very large number of Access Points (AP). A variety of other wireless networks have been installed, such as cellular and other wireless networks. Some wireless networks are based upon the Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of industry specifications, such as specifications for IEEE 802.11b, IEEE 802.11g and IEEE 802.11a, etc. A number of working groups are working to improve on this technology or family of specifications.
A High Throughput WLAN standard known as IEEE 802.11n has proposed a media access control (MAC) frame aggregation technique to aggregate multiple MAC service data units (MSDUs or MAC data frames). Multiple MAC frames or MSDUs, e.g., having a same destination address, may be aggregated together into a single MSDU (A-MSDU), with additional fields inserted into the resulting aggregated frame. In this manner, additional efficiency may be obtained by eliminating some duplicative overhead for the multiple MSDUs. The Enhanced Wireless Consortion (EWC) has proposed a similar MAC aggregation in the EWC High Throughput (HT) MAC Specification, V1.0, Sep. 12, 2005.
In addition, a draft specification from the IEEE 802.11e Task Group has proposed a set of QoS parameters to be used for traffic delivery between an Access Point (AP) and a station in a wireless network. Under the 802.11e draft specification, different channel access mechanisms are proposed, including a contention based channel access and a polled based channel access. According to the 802.11e draft specification, Enhanced Distributed Channel Access (EDCA), for example, provides a contention based channel access mechanism that differentiates between different traffic classes (Access Categories or AC). According to EDCA, a different set of parameters (such as a contention window size or CW and a minimum period of time to sense an idle medium before transmitting) may be provided for each AC. By using a different set of access and contention parameters for each access category (AC), this may change the probability of obtaining or contending for access to the channel to favor higher priority ACs (traffic classes).
Different types of traffic may have different delay requirements. For example, best-efforts traffic may not have strict delay requirements. However, other types of traffic, such as conversational services (e.g., voice over IP or VoIP) may have stricter delay requirements since frames may typically not be played after their playout or delay time.
The 802.11e draft specification also provides a transmit timer for each MAC frame (or MSDU). A wireless node (e.g., wireless station or access point) may maintain a transmit timer for each received MAC frame or MSDU. A parameter known as MSDULifetime (or Lifetime) may indicate a maximum transmission delay over air interface frame delivery, from wireless node 1 to wireless node 2, for a traffic stream or AC. The transmit timer may be set or started when a frame is received at the MAC. According to the 802.11e draft specification, if the value of the transmit timer for the frame or MSDU exceeds the Lifetime (or delay bound), then the frame is discarded without further attempt to deliver the frame.
However, current proposals do not specify how the frame aggregation mechanisms may relate to or operate with the Lifetime values or with different access categories (ACs).